In European patent application 24758, a process for oxidative biological purification of waste water is disclosed, whereby the waste water flows in an upward direction through an oxidation chamber in which microorganisms are present, attached to an insoluble carrier. The function of the carrier is to support the active sludge by providing a surface for sludge to grow on and/or to increase the density of the sludge-carrier particle. Separation of the purified waste water from the supported active sludge takes place at the top of the reactor and separated sludge is returned to the reactor.
In these type of reactors, also known as airlift reactors, movement of the suspension in the oxidation reactor is provided by introduction of oxygen, air or oxygen enriched air. At the top of the oxidation chamber the three phase mixture, consisting of water, gas and supported sludge is separated in a three phase separator.
Part of the recirculating waste water is separated from the supported activated sludge and is removed from the reactor as effluent. All, or at least a majority of the sludge is recirculated to the reactor, usually in a compartment in which there is a downward flow. This may be, but is not necessarily an anaerobic or anoxic zone.
It is an object of the invention to provide an improved process or system for the aerobic purification of waste water of the type described herein above.